Natural and abundant plant triterpenoids are attractive starting materials for the synthesis of conformationally rigid and chiral building blocks for functional soft materials. Here, we report the rational design of three oleanolic acid-triazole-spermine conjugates, containing either one or two spermine units in the target molecules, using the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. The resulting amphiphile-like molecules 2 and 3, bearing just one spermine unit in the respective molecules, self-assemble into highly entangled fibrous networks leading to gelation at a concentration as low as 0.5% in alcoholic solvents. Using step-strain rheological measurements, we show rapid self-recovery (up to 96% of the initial storage modulus) and sol ⇔ gel transition under several cycles. Interestingly, rheological flow curves reveal the thixotropic behavior of the gels. To the best of our knowledge, this kind of behavior was not shown in the literature before, neither for a triterpenoid nor for its derivatives. Conjugate 4, having a bolaamphiphile-like structure, was found to be a nongelator. Our results indicate that the position and number of spermine units alter the gelation properties, gel strength, and their self-assembly behavior. Preliminary cytotoxicity studies of the target compounds 2-4 in four human cancer cell lines suggest that the position and number of spermine units affect the biological activity. Our results also encourage exploring other triterpenoids and their derivatives as sustainable, renewable, and biologically active building blocks for multifunctional soft organic nanomaterials.

Department of Applied Physics Aalto University Puumiehenkuja 2 FI 02150 Espoo Finland

Department of Chemistry of Natural Compounds University of Chemistry and Technology Prague Technická 5 16028 Prague 6 Czech Republic

Department of Chemistry University of Jyväskylä P O Box 35 FI 40014 Jyväskylä Finland

Faculty of Engineering and Natural Sciences Tampere University P O Box 541 FI 33101 Tampere Finland

Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences Flemingovo náměstí 2 16610 Prague 6 Czech Republic

Institute of Physics Faculty of Mathematics and Physics Charles University Ke Karlovu 5 12116 Prague 2 Czech Republic

Isotope Laboratory Institute of Experimental Botany of the Czech Academy of Sciences Vídeňská 1083 14220 Prague 4 Czech Republic

Laboratory of Growth Regulators Institute of Experimental Botany of the Czech Academy of Sciences and Faculty of Science Palacký University Šlechtitelů 27 CZ 78371 Olomouc Czech Republic

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